1. Field of the Invention
The present invention relates generally to liquid crystal display devices, and more particularly to a vehicular, compact liquid crystal display device slimmed down in bezel region size for increased display region.
2. Description of the Related Art
A conventional liquid crystal display device include: a thin-film transistor (TFT) substrate formed with pixel electrodes, TFTs, and other elements in matrix form; a counter substrate disposed in facing relation with respect to the TFT substrate and formed with a color filter and other elements at locations corresponding to the pixel electrodes on the TFT substrate; and liquid crystals arranged between the TFT substrate and the counter substrate. The display device forms images by controlling, on a pixel-by-pixel basis, transmittance of light formed by the liquid-crystal molecules.
Liquid crystal display devices can be made compact and lightweight, so that their applications are expanding in a wide variety of products, including TVs, cell phones, and many more. Recently, they also are commonly used as vehicle-mounted types of displays. For vehicular application, since vibration and the like are exerted, they require more effective anti-vibration preventive measures than those required in a normal type of liquid crystal display device.
In addition to being exposed to a vibration-prone environment, vehicular types of liquid crystal display devices are used in a wide environmental temperature range from −30° C. to +85° C. Heat-related preventives are therefore necessary. Optical sheets, in particular, have a problem in that it swelling or waviness is caused by thermal expansion under a high-temperature atmosphere, the sheet will not return to a normal stare even after being cooled down. By way of example for comparison, displays for medical monitors range between 0° C. and +60° C. in operating environmental temperature.
Vehicular liquid crystal display devices further need to be placed in a limited space. Since liquid crystals do not emit light themselves, a backlight is disposed in the back of a liquid crystal display panel. Disposing the backlight in a limited space requires downsizing a light source, so light-emitting diodes (LEDs) are used as the light source. These LEDs are arranged on a side of a light guide plate, then various optical sheets are arranged on the light guide plate, and these optical parts are accommodated in a mold, whereby the backlight is constructed.
JP-A-2008-46430 describes a configuration that includes a light guide plate having a sloped surface to increase the amount of incidence of light from LEDs by arranging the LEDs on a side of the light guide plate that is thicker than any other section of the light guide plate.